A plastic magazine and trigger, which could have potentially been fitted together to make a gun, were seized by police in Manchester along with the 3D printer that created them.
The components are now being examined to see if they could have been fitted together to make a viable 3D gun.
The technology works by allowing anyone with a 3D printer - which can be bought on the high street for £1,200 - to download designs for guns or components.
A man has been arrested on suspicion of making gunpowder and remains in custody for questioning, Greater Manchester Police said.
More top news
The US Navy says 10 sailors are missing and five are injured after the USS John S. McCain collided with a merchant ship near Singapore
The Crown Prosecution Service says the internet has provided "new platforms for offending behaviour"
A Public Health England report estimated 150,000 to 200,000 Britons are infected with the virus by imported pork every year.